1. Field of the Invention
The invention belongs to the mechanical arts. Specifically, the invention lies in the field of roller bearing lubrication in printing technology. The invention, in particular, relates to bearings for printing rollers and a method of lubricating the printing roller bearings.
Printing machines typically operate with a multiplicity of rollers that form nips through which product travels. The product may be a continuous web or individual sheets of paper or cardboard to be printed.
The rollers in the printing machines are supported in lubricated roller bearings. The roller bearings are conventionally lubricated with grease that is supplied from a grease reservoir. Typically, a grease pump enables sporadic pumping of the grease from the reservoir through various grease lines and into strategic locations in the bearings.
2. Description of the Related Art
U.S. Pat. No. 5,484,212 to Guaraldi et al., which is commonly assigned, discloses a method of lubricating a printing cylinder bearing in which an air jet is used to distribute the grease that is pumped into the bearing from a grease reservoir. A printing cylinder is supported by a roller bearing with rolling elements that support mutually opposed bearing race surfaces. In addition to distributing the grease on the rolling elements of the roller bearing, a small amount of grease is axially injected towards the cylinder body, where it forms a grease seal between the bearing housing and the cylinder.
Depending on the speed of the printing unit and/or the associated product-processing system, the rollers rotate at substantial speeds. For instance, blanket cylinders and plate cylinders in offset lithographic printing machines rotate in excess of about 1100 rpm. Lubrication with grease is inadequate to properly remove the buildup of friction heat in the bearings of such cylinders. The art therefore effects a heat exchange with cooling plates attached to the bearing housings. The cooling plates are cooled down by heat exchange with chilled cooling water.
The cooling water supply is a relatively complicated and expensive system. A proper flow and temperature of the cooling water must be ensured so as to assure proper heat exchange. Furthermore, lubrication with grease is not recommended by bearing manufacturers at high speeds. Instead, oil lubrication is recommended.